1. Technical Field
The present invention relates to methods of making a prosthesis with a smooth covering.
2. Background Information
Some medical prostheses, such as stents, include material, fabric or a graft to cover the prosthesis. Covered stents include a stent graft that includes fabric or other material that covers and is supported by a stent. Covered stents are manufactured by different methods. One method includes placing the stent on a mandrel between shells of a pressure applicator. The pressure applicator may include two halves or multiple components that form a cavity with a circular cross section. Each component of the pressure applicator may contain one or more layers of material for application to the stent. When the components of the pressure applicator are brought together to cover the stent, the resulting covered stent may have visible creases where the components meet. The creases create a lack of continuity in the material covering the stent and may cause premature failure of the material or an area that may catch on a vessel or collect undesirable material.
Other methods of manufacturing covered stents include using shrink tubes and/or tubing that are off the shelf and readily available to attach the fabric or graft on the stent. For example, covered stents have been made using off the shelf silicone tubing having a high durometer, such as high durometer silicone tubing including silicone tubing with a durometer of 50-70 Shore A. Manufacturers identify silicone tubing having a durometer of 50-70 Shore A as soft and silicone tubing having a durometer of 35-45 Shore A as very soft, both of which are readily available from manufacturers. Silicone tubing with a lower durometer is not readily available from manufacturers.
These methods to make covered stents using shrink tubes, tubing having a high durometer, and/or sheets of material having a high durometer to attach the fabric or graft on the stent may create visible creases or ridges that form on the graft of the stent, which create a lack of continuity on the stent. Previously used pressure methods also cause the struts of the stent to deform or distort when the shrink tubes or high durometer tubes are applied to the fabric and the stent because higher deformation forces and displacement of the tubes is needed to compress the fabric or graft around the struts of the stent for bonding. In addition, when using these methods, the fabric or graft is not able to conform to the struts of the stent, or otherwise profile the struts of the stent, to create a smooth covering over the stent.